The overall objective of this proposal is to identify proteins or protein pathways that mediate critical aspects of mammary tumor progression and to develop screens for small molecule inhibitors of these pathways. This will be accomplished using a functional genomics approach that involves infecting mammary epithelial cells with libraries of retroviruses encoding candidate tumor progression genes and screening for cells that display various properties of tumor cells in culture. The genes responsible for these phenotyping alterations will then be identified and cloned. We will then validate these genes as potential therapeutic targets based on whether these genes are altered in sequence or expression in breast tumors. Once validate targets are identified, we will then collaborate with the Institute of Chemistry and Cell Biology (ICCB) and industry to identify candidate small molecule modulators of these critical targets. The functional assays developed for this project provide the means to screen through large numbers of genes from breast tumor cells in order to identify genes that are able to mediate phenotypic alterations associated with tumor progression. The assays will be used in screens to identify novel genes from breast tumor cells, in establishing which properties of mammary tumor cells are regulated by known associated with breast cancer and in determining whether genes identified through high throughput expression analysis of breast tumor cells can mediate phenotypic alterations in mammary cells. Collaboration with other SPORE projects will be critical in providing genes for analyzing and for analyzing tumor samples to evaluate the relevance of the genes to human breast cancer. Lastly, through collaborations with the ICCB and industry, we plan to translate these findings into meaningful interventional strategies through the development and execution of screens for small molecule inhibitors that will interfere with breast cancer progression.